Challenge.java

import java.util.Arrays;
import java.util.Scanner;

class CoderbyteLongString {

    private static final String REGEX = "[^0-9+a-z+A-Z ]*";

    public static String LongestWord(String sen) {
        String[] words =
                sen.replaceAll(REGEX, "") //filter out any characters that aren't a normal letter or number - remove punctuation
                        .split(" "); // Split the filtered string into words

        return Arrays.stream(words) //Create a Stream (a kind of fancy list) of all of the words
                .filter(s -> !s.isEmpty()) //remove any entries in the stream if it's empty. I don't think they should be but just in case
                .sorted((s1, s2) -> Integer.compare(s2.length(), s1.length())) //Sort all of the words in order of their length, but backwards, so a Stream of ["I", "love", "dogs"] will become ["dogs", "love", "I"]
                .findFirst().get(); //find the first entry in the Stream (in our case "love")  and that's the answer
    }

    //Default stuff for running and parsing input
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.print(LongestWord(s.nextLine()));
        s.close();
    }

}